When smoking in a conventional manner, there is generally understood to be three types of cigarette smoke, mainstream smoke, exhaled smoke and sidestream smoke. There has been significant interest in reducing the amount of sidestream smoke emitted by a burning cigarette or cigar because it accounts for the majority of smoke emitted during the smoking process. Attempts have been made to control sidestream smoke by one or more of the following techniques:    1) alter the tobacco composition and packing characteristics of the tobacco rod or charge in the cigarette or cigar;    2) alter the wrapping for the cigarette or cigar;    3) alter the diameter of the cigarette as well as its tobacco composition; and/or    4) provide a device on the cigarette or cigar to contain and/or control sidestream smoke emissions.
Various cigarette tobacco and cigarette paper formulations have been suggested which in one way or another affect the free-burn rate of the cigarette or cigar with a view to reducing sidestream smoke and/or achieving an extinguishment of the lit cigarette or cigar when left idle over an extended period of time. Such designs include a judicious selection of tobacco blends, density and multiple layers of cigarette tobacco in the tobacco charge. Such selected designs can appreciably retard the free-burn rate of the cigarette and hence, increase the number of puffs obtained per unit length of cigarette. Either in combination with tobacco selection and/or construction or independently of the tobacco make up, various cigarette paper compositions can also affect free-burn rate of the cigarette. Such paper compositions include the use of chemicals to retard free-burn rate, multiple wrappings of different types of cigarette paper of the same or different characteristics and reduction of air permeability. See for example, Canadian Patent 1,259,008 and U.S. Pat. Nos. 4,878,507 and 4,915,117.
Various devices have been provided which contain the cigarette, primarily for purposes of preventing accidental fires. They may or may not at the same time include various types of filters to filter and thereby reduce the amount of sidestream smoke. Examples of such devices are shown in U.S. Pat. Nos. 1,211,071; 3,827,444 and 4,685,477.
Further, various types of cigarette holders have been made available which service the primary feature of minimizing staining of the smoker's fingers. Such devices may be connected to the cigarette tip and/or mounted on the cigarette, such as shown in U.S. Pat. No. 1,862,679. Other types of cigarettes which are enclosed in wrappers which are perforated in one way or another to provide for safety features and/or control of sidestream smoke are described in Canadian Patent 835,684 and U.S. Pat. Nos. 3,220,418 and 5,271,419.
Devices which are mountable on the cigarette and which may be slid along the cigarette to control combustion and hence free-burn rate are described in U.K. Patent 928,089; U.S. Pat. No. 4,638,819 and International application W096/22031. The U.K. patent describes a combustion control device for cigarettes by limiting the flow of air to the cigarette burning ember. By retarding combustion of the cigarette, it is suggested that only half of the conventional amount of tobacco need be incorporated in the cigarette and result thereby in a shorter cigarette. The air flow limiting device may be provided by an array of apertures in the device with variable opening or by crimped portions in the device providing longitudinal openings along part of the cigarette. U.S. Pat. No. 4,638,819 describes a ring which is placed on the cigarette and slid therealong during the smoking process to control the free-burn rate of the cigarette and reduce sidestream smoke. The ring is of solid material, preferably metal, which causes considerable staining and due to variable cigarette diameters cannot reliably provide the desired degree of sidestream smoke reduction and extinguishing times.
An alternative ring system is described in applicant's published PCT application WO 96/22031. The device is provided with an inner ring which surrounds and contacts a conventional cigarette perimeter where the inner ring is of porous material. The outer ring encases the inner ring to direct air flow along the length dimension of the porous inner ring. The tortuous paths in the porous material of the inner ring controls the rate of air diffusion to the lit cigarette coal and thereby controls the free-burn rate of the cigarette. The porous material enhances the control of sidestream smoke emitted by the lit cigarette. The device may optionally extend up to one-half the length of the cigarette where air would have to flow along the inner porous ring to the burning coal.
Other systems which have been designed to control sidestream smoke are described in published PCT application WO 95/34226 and U.S. Pat. No. 5,592,955 issued Jan. 14, 1997 and U.S. Pat. No. 5,105,838 issued Apr. 21, 1992. These references describe various tubular configurations in which a tobacco element is placed in an attempt to minimize cigarette sidestream emission.
Although these approaches may have met with various degrees of success, in controlling sidestream smoke emissions, there are problems with some of the devices in providing conventional taste and flavor, ease of use, ease of manufacture, streamline appearance and significant reductions in the amount of tobacco used. The various embodiments of this invention provide a device which overcomes a number of the above problems by controlling both sidestream smoke and free-burn rate while achieving taste, flavor and constituent deliveries comparable to conventional cigarettes. The device of this invention permits the smoking of a thinner cigarette which has only as much tobacco as is necessary to deliver the desired taste while achieving the conventional number of puffs.
In order to facilitate the description of the invention, the term tobacco charge shall be used in referencing a cigarette, cigar, cigarillo, tobacco rod in a porous mesh, a tobacco plug or wrapped tobacco or the like. It is also understood that where the term cigarette is used, it is interchangeable with cigar, cigarillo and the like.